Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 29-01-2013, 01:44   #31
Registered User
 
Bluewaters2812's Avatar

Join Date: Sep 2012
Location: Cruising
Boat: Not a Beneteau!
Posts: 911
Images: 1
Send a message via Skype™ to Bluewaters2812
Re: True or Magnetic for Electronic Nav.

Quote:
Originally Posted by LJH View Post
Reminds me of the old saying "measure it with a micrometer and cut it with an axe!
I guess somewhere along the line where the axe makes the cut, it will be exactly spot on with the micrometer (provided the axe wielding assailant can aim). But we digress.
__________________

__________________
Bluewaters2812 is offline   Reply With Quote
Old 29-01-2013, 01:53   #32
CF Adviser
 
Pelagic's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 6,890
Re: True or Magnetic for Electronic Nav.

Looks like the professional mariners on this thread seems to agree that correcting any compass to True is standard procedure. Forget about Gyro’s and sat Compasses for now

It is not hard to do on a yacht given that:
Flux Gate compasses can display True Hdgs, and automatically update variation factors when tied to the GPS

Automatic Deviation Calibrations are easy to do after you have changed the stereo, or bought your girl some bling

Today with all the electronics, Ipods and wiring near the helm… your standard magnetic compass is purely an emergency reference tool to monitor and log Compass headings with your known True Course.
(Just in case you ever have to actually steer by it.)

We no longer trust them to orient the autopilot AP using a sonde…
instead yachts now use Fluxgates, buried away in some stable place

Reasons why I think using True Headings is easier:
  • Range Lights and other Leads are shown in True…easy to constantly verify your AP Flux compass while noting D&V on steering Compass.
  • In ColReg Communication with other boats you don’t give Relative/Reciprocal Bearing in Magnetic or Compass, but in True… (Aspect is different)
  • My Chart Program or paper charts display North-Up meridians
  • My Radar is set to North-up… which helps to stabilize display
  • My GPS gives Bearings in True as does an AIS, if you have one.
Basically 3 am on a hazy morning if someone on watch is confused with the reliability of bearings they are using … it will not be me as I have a few natural and electronic ways to check it all in True
__________________

__________________
Pelagic is online now   Reply With Quote
Old 29-01-2013, 02:01   #33
LJH
Registered User

Join Date: Mar 2012
Location: Nova Scotia
Boat: Wauquiez Centurion 42
Posts: 274
Re: True or Magnetic for Electronic Nav.

Quote:
Originally Posted by Ship2210 View Post
Either system will work but for me, as a private pilot I was taught to use true and apply the magnetic variation. I have always used that since and it is 2nd nature to me. I enjoy "the fun" of being aware of what the variation is wherever you are positioned in the world.
Ah yes, "Variation East, Magnetic Least..." Whichever system you use you should be aware of the variation and your compass deviation as it does not take much to be a compass only boat when you least expect it.
__________________
LJH is offline   Reply With Quote
Old 29-01-2013, 02:12   #34
Registered User

Join Date: Feb 2012
Posts: 2,441
Re: True or Magnetic for Electronic Nav.

A further reason to prefer Truth over Magnetism:

if you're a sailor, the wind direction is expressed as True, never Magnetic.

In my part of the world a NNE wind comes from magnetic North, and that's way too much mental gymnastics for this kid, on top of the need to figure True wind from apparent.

Imagine working out your heading in degrees M if the wind is expected to fill in from the SW and you'll be close hauled on starboard and the variation is 16degW: quickly, anyone ? (in True, it takes about 2 sec with eyes closed to figure it's basically S)

Which highlights another issue: if you decide to live in a Magnetic world, what would you call True wind direction (as distinct from Apparent)?

"True Magnetic"?

I don't think so....

Apart from this, and the other good reasons given above, such as charted channel axes, leads etc...

I think anyone voyaging would do well to stick to True, because otherwise their thinking is not grounded to anything constant as they move about in terms of location, and hence variation.

(or time, for that matter - which of course is why published bearings are always in True)
__________________
Andrew Troup is offline   Reply With Quote
Old 29-01-2013, 02:28   #35
CF Adviser
 
Pelagic's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 6,890
Re: True or Magnetic for Electronic Nav.

Quote:
Originally Posted by Andrew Troup View Post
A further reason to prefer Truth over Magnetism:
Yes we don’t want those fuzzy marine lawyers confusing Truth with courtroom Magnetism
__________________
Pelagic is online now   Reply With Quote
Old 29-01-2013, 12:33   #36
Registered User

Join Date: Feb 2012
Posts: 2,441
Re: True or Magnetic for Electronic Nav.

I've thought some more about this, and I now feel more strongly than I did before thinking it through.

I'm less comfortable than I was about settling for Magnetic North as one's habitual datum.

Firstly, because it means delegating to technology a job which I think is too important to habitually leave to "others": in this case, allowing for Variation.

One risk of doing so is that one day, we will assume it is being done, only to find -too late - that it has not.

(probably not because of a technology failure, but because circumstances have changed: we're on someone else's boat, or we're relying on unfamiliar aids in an emergency, or whatever).

It's a bit like relying on your remote to lock your car, instead of doing it manually.

All it takes is one loose connection for one door to remain unlocked.

If you have to check all the doors yourself, the technology is not providing any added value: you might just as well lock them yourself.

OK, a car is only a car, so it's a tradeoff we are all happy to make.

But a navigational error is not just possibly going to lose us a boat, it might lose us our life, or worse.

I'm pretty sure I'd be checking the doors were all locked the old fashioned way, if a homicidal maniac was circling the car.

- - - - - - - - - -

Secondly because adopting a Magnetic mindset means we're swimming metaphorically in an isolated pool, in terms of how we handle geographical information.

It has been pointed out that it makes it harder to use information from the past (sailing directions, pilots, cruising guides, historical accounts etc)

but it also makes any notes we take risky for the future - particularly in places where variation changes quite quickly, and sailors live quite long.

That is, unless we note against each bearing we record, not only the fact that it was magnetic, but the year when we measured it, or better still, the variation at that time.

Idea: why not note it down in degrees True?

- - - - - - - - -

Thirdly, I think it's a good idea to train one's sense of 'situational awareness' over one's lifetime by developing the habit of regularly taking notice of things like:

- the direction of the sun when it reaches the highest point it its daily arc (not just at sea, but from familiar locations on land) which is obviously true North

- the direction of the sun rising and setting at the equinox, which almost as obviously is true East and true West

- the way that latter direction changes during the year, as a function of latitude, some aspects of which are quite counterintuitive

Having such habits means we can easily use the sun as a crude compass, and this can be a major help when cut adrift from technological direction-finding aids, on land or at sea.

Even with technological aids, the sun can occasionally be useful: I used it recently when I was lent a hand-held GPS for a land-based mission of resupplying tracking tunnels for pest species.

It was new to the person lending it to me, so they had mis-described how to use the direction-finding capabilities; the method they told me was applicable to the previous model, but once I was on task it was giving meaningless behaviour with this unit.

For those muttering "RtFM", there was no "M" to "FR", and neither cellphone nor coverage.

I was able to instead refer to the approximate bearing to the next waypoint, given as (say) "NW", and (not having a compass) use the sun to tell me roughly where that was.

Given that I knew the exact distance to the waypoint, knowing the rough direction saved me from having to traverse a lot of extra distance, sometimes through rather impenetrable and even hostile ground cover. Probably saved nearly a day, and lots of scratches and nettle stings.


It seems to me that such a 'situation awareness' mindset needs to be based on having True North as the dominant reference, and Magnetic in a subsidiary role.
__________________
Andrew Troup is offline   Reply With Quote
Old 29-01-2013, 15:21   #37
Registered User

Join Date: Nov 2011
Location: Fethiye Turkey
Boat: Lagoon 440
Posts: 3,164
Re: True or Magnetic for Electronic Nav.

I too have been thinking more on this and tend to agree with Andrew.
WARNING LIGHTHEARTED:-
1) This thread is for those who do use paper charts.

2) A carpenter i know quite well took the re-coil spring off his 9inch circular saw guard leaving it to be pushed back in place each time he used the saw, i asked him why he did this?

He said 'We all become slack on relying on things it's far better to reset the saw guard every-time knowing it wont protect rather than supposing it will'
My return comment was 'what about the innocent one who pick's up your saw only to get severely cut?'

Cheers
__________________
"Political correctness is a creeping sickness that knows no boundaries"
Lagoon4us is offline   Reply With Quote
Old 30-01-2013, 03:10   #38
Registered User
 
Bluewaters2812's Avatar

Join Date: Sep 2012
Location: Cruising
Boat: Not a Beneteau!
Posts: 911
Images: 1
Send a message via Skype™ to Bluewaters2812
Re: True or Magnetic for Electronic Nav.

Quote:
Originally Posted by LJH View Post
Ah yes, "Variation East, Magnetic Least..." Whichever system you use you should be aware of the variation and your compass deviation as it does not take much to be a compass only boat when you least expect it.
__________________
Bluewaters2812 is offline   Reply With Quote
Old 30-01-2013, 05:54   #39
Long Range Cruiser
 
MarkJ's Avatar

Cruisers Forum Supporter

Join Date: Dec 2007
Location: Australian living on "Sea Life" currently in England.
Boat: Beneteau 393 "Sea Life"
Posts: 12,828
Images: 25
Re: True or Magnetic for Electronic Nav.

Quote:
Originally Posted by Pelagic View Post
Today with all the electronics, Ipods and wiring near the helm… your standard magnetic compass is purely an emergency reference tool to monitor and log Compass headings with your known True Course.
(Just in case you ever have to actually steer by it.)
I agree and agree with this whole post and advise those newer to cruising and long passages to read it carefully.


It is vital to me to be sailing in the safest possible manner. That can only be with good use of electronics.

Yes a compass is still necessary on the binnacle, but the next one I buy wont be the lickerty-split expensive big ones that formerly held pride of place at the wheel. Now a small one is suitable for emergency and the occasional glance to check difference between the Fluxgate compass of the Auto Pilot.
__________________
Notes on a Circumnavigation.
OurLifeAtSea.com

Somalia Pirates and our Convoy
MarkJ is offline   Reply With Quote
Old 30-01-2013, 06:27   #40
LJH
Registered User

Join Date: Mar 2012
Location: Nova Scotia
Boat: Wauquiez Centurion 42
Posts: 274
Re: True or Magnetic for Electronic Nav.

Quote:
Originally Posted by MarkJ View Post
I agree and agree with this whole post and advise those newer to cruising and long passages to read it carefully.


It is vital to me to be sailing in the safest possible manner. That can only be with good use of electronics.

Yes a compass is still necessary on the binnacle, but the next one I buy wont be the lickerty-split expensive big ones that formerly held pride of place at the wheel. Now a small one is suitable for emergency and the occasional glance to check difference between the Fluxgate compass of the Auto Pilot.
I can only partially agree with you Mark. What is vital is learning the basics in the first place. Learn to sail with a compass, learn to listen to your boat when it talks to you (don't wear an iPod at the helm!), learn to hand steer and learn how to use a paper chart. Electronics are one of the tools available to use when sailing - not the only tool! Learn the basics and learn to electronics properly and you will have a good tool box!

You don't need electronics to go from A to B, but they will help you get there safely. They may fail for a multitude of reasons, so you must always be prepared and able to take over manually at any time. It should still be possible to get there safely without the electronics.
__________________
LJH is offline   Reply With Quote
Old 30-01-2013, 06:52   #41
Registered User
 
LakeSuperior's Avatar

Join Date: Jan 2008
Boat: Teak Yawl, 37'
Posts: 1,581
Images: 7
Re: True or Magnetic for Electronic Nav.

For a number of reasons I do all the navigation in true.

At the helm you steer the compass course making short time constant small continuous course changes.

However, I derive the compass course iteratively by watching the GPS which has a longer time constant and so that I maintain my desired true course.

Essentially, I am somewhat lazy and doing everything magnetic is too much thinking. Also, we found on long passages that the magnetic variation varys.

One other factor to consider that goes into the SAFETY department. If an electronic piece of gear is left unwittingly near the compass and it causes a local shift in the magnetic field and the compass will point in the wrong direction. It is impossible to realize this shift in heading unless the GPS is consulted for verification of the course. Using the above approach this problem will be caught instantly.
__________________
LakeSuperior is offline   Reply With Quote
Old 31-01-2013, 01:07   #42
CF Adviser
 
Pelagic's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 6,890
Re: True or Magnetic for Electronic Nav.

Quote:
Originally Posted by LJH View Post
....What is vital is learning the basics in the first place. Learn to sail with a compass,....
LJH… I agree, I think if a reader is not proficient with basic navigation techniques and practices they have no business being on the water.

However, in this discussion, if you consider the basic compass terminology
  • “Correcting” is converting a magnetic (M) direction to true (T).
  • “Un-correcting” is converting from true to a magnetic direction.
Then you have to ask yourself….do I want to finish my calculations with something that is correct or un-correct?

That is why True Course is the accepted navigational standard once you have learned the basics.

25 years ago I sailed the world with compass and sextant.... today I have electronic Nav-tools far more accurate and I use them to "correct" the Compass
__________________
Pelagic is online now   Reply With Quote
Old 31-01-2013, 03:12   #43
LJH
Registered User

Join Date: Mar 2012
Location: Nova Scotia
Boat: Wauquiez Centurion 42
Posts: 274
Re: True or Magnetic for Electronic Nav.

Quote:
Originally Posted by Pelagic View Post
LJH… I agree, I think if a reader is not proficient with basic navigation techniques and practices they have no business being on the water.

However, in this discussion, if you consider the basic compass terminology
  • “Correcting” is converting a magnetic (M) direction to true (T).
  • “Un-correcting” is converting from true to a magnetic direction.
Then you have to ask yourself….do I want to finish my calculations with something that is correct or un-correct?

That is why True Course is the accepted navigational standard once you have learned the basics.

25 years ago I sailed the world with compass and sextant.... today I have electronic Nav-tools far more accurate and I use them to "correct" the Compass
__________________
LJH is offline   Reply With Quote
Old 31-01-2013, 03:58   #44
cruiser

Join Date: Dec 2012
Location: Seattle
Posts: 1,130
Re: True or Magnetic for Electronic Nav

I've never seen a reason to use true. I still don't.
__________________
Jammer Six is offline   Reply With Quote
Old 31-01-2013, 13:20   #45
Senior Cruiser
 
Jim Cate's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 11,454
Re: True or Magnetic for Electronic Nav.

Quote:
Originally Posted by Pelagic View Post

However, in this discussion, if you consider the basic compass terminology
  • “Correcting” is converting a magnetic (M) direction to true (T).
  • “Un-correcting” is converting from true to a magnetic direction.
Then you have to ask yourself….do I want to finish my calculations with something that is correct or un-correct?

That is why True Course is the accepted navigational standard once you have learned the basics.
Just curious: where in the world did you find this "basic compass terminology"?

And your leap to your conclusion is mind boggling to me!

I reckon that the reason that ships navigate with true courses is because they have gyro compasses which can read out directly in True. With that ability there is no reason to use magnetic headings.

But for those of us who still rely upon magnetic compasses, well, I guess we'll just have to bear the shame of using "uncorrect" headings.

Jim
__________________

__________________
Jim and Ann s/v Insatiable II , lying Port Cygnet, Tasmania once again
Jim Cate is online now   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Charts II: NGA - 2700 Charts cagney OpenCPN 1292 23-12-2013 09:46
For Sale: BRISTOL 45.5 DESTINY avail. for viewing in South FL sail_destiny Classifieds Archive 7 17-01-2013 10:04
Differences Between Ground, Apparent, and True Wind Direction twistedtree Navigation 92 26-12-2011 14:48
True North or Magnetic North ? Mary Farmer OpenCPN 24 31-10-2011 13:39



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 20:07.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.